This K08 award application is designed to enrich the candidate's career development in the epidemiology of gastrointestinal diseases. The program integrates mentored "hands on" experience in the proposed research plan on inflammatory bowel disease (IBD), didactic coursework to advance the knowledge and skills of the candidate, and enhanced interactions with other investigators through seminars, conferences, and scientific meetings. In the later years of the 5-year proposed program, the candidate plans to expand her work in the epidemiology of pediatric gastrointestinal illnesses. The candidate's sponsor is Dr. Richard J. Grand, an accomplished pediatric gastroenterologist with significant established experience in the field of IBD. Her co-sponsor is Dr. Graham A. Colditz, the Principal Investigator of the Nurses' Health Study at the Channing Laboratory. The program combines the institutional resources of the Children's Hospital, Boston and the Channing Laboratory of the Brigham and Women's Hospital, Harvard medical School. The Research proposal is a prospective cohort study to examine the association of environmental factors and the two types of IBD, Crohn's disease (CD) and ulcerative colitis (UC). The study base population will be composed of the Nurses' Health Study (NHS I) and the Nurses' Health Study II (NHS II) cohorts. Specific Aim 1 is to establish a database of confirmed cases of CD and UC in the NHS I and NHS II cohorts. Specific aims 2 through 4 will examine the association of specific dietary factors, smoking, and exogenous estrogen therapy and the development of CD or UC. Since the establishment of the NHS I in 1976 and the NHS II in 1989, information pertaining to participants' dietary intake and lifestyle factors has been updated at regular intervals, prior to the onset of CD or UC. Cases of CD and UC will be identified by biennial questionnaires and confirmed by medical chart review using established criteria. Analyses will compare age-specific incidence rates of CD and UC within different exposure categories, multivariate analyses, using the Cox proportional hazards model, will be performed. The proposed study will establish a unique database of repeated dietary and lifestyle assessments over several decades and will provide the opportunity to examine the influence of nutritional and lifestyle risk factors on IBD risk, improve our understanding of IBD pathogenesis, and define potential methods of prevention.